Let's do some math ..  Rounding examples of 7 random hypothetical purchases:
  Case Tag  
Price  
Sales  
Tax %  
Raw Total  
Incl. Sales Tax  
Rounded  
to Penny  
Rounded  
to Nickel  
Rounded  
to Dime  
  Purchase #1 $56.91   9.752%   $62.4599   $62.46   $62.45   $62.50  
  Purchase #2 $166.52   6.462%   $177.2805   $177.28   $177.30   $177.30  
  Purchase #3 $31.63   4.854%   $33.1653   $33.17   $33.15   $33.20  
  Purchase #4 $65.77   8.253%   $71.198   $71.20   $71.20   $71.20  
  Purchase #5 $85.77   13.644%   $97.4725   $97.47   $97.45   $97.50  
  Purchase #6 $59.78   5.409%   $63.0135   $63.01   $63.00   $63.00  
  Purchase #7 $191.64   10.206%   $211.1988   $211.20   $211.20   $211.20  
  7 purchase totals = $658.02       $715.7885   $715.79   $715.75   $715.90